A. You may be grossing out your friends — some people consider the sound of cracking knuckles as odious as fingernails on a blackboard — but you are causing no harm to yourself, according to Dr. Andrew Terrono, chief of hand surgery at New England Baptist Hospital.

Terrono said patients ask him this question all the time, and he tells them that the latest research suggests cracking knuckles will not cause arthritis or damage ligaments.

The sound is actually bubbles of nitrogen popping, he said. When you pull on your joint, you create a vacuum, pulling nitrogen bubbles out of the joint and causing them to pop, he said.

“Some people can do it more than others,” Terrono said. “I don’t think anyone knows why.”

There are some medical conditions that mimic the cracking of knuckles and may be more bothersome, he said, such as trigger finger, in which the finger makes a snapping noise and doesn’t straighten easily. “If it bothers them a lot then we treat it,” he said.

One scientist, who had been harangued about his knuckle-cracking habit, decided to take matters into his own hands. For the next 60 years, at least twice a day, Dr. Donald Unger systematically cracked the knuckles on his left hand but not his right. When he compiled his data, he found no apparent difference between the hands, and no arthritis in either.

In 2009, the California doctor, then 83, traveled to Cambridge to accept an Ig Nobel award, given for science that “first makes people laugh and then makes them think.” In accepting, he waved his hands in mock rebellion against his mother, according to news reports at the time.